SERS Substrates Research Articles

Rapid determination of thiram in lake water using Au/Fe3O4 nanoparticles decorated MOF-867 as efficient surface-enhanced Raman scattering substrate

Rapid determination of pesticide residues in water is of vital importance for human health. However, rapid, reliable, and highly sensitive detection of pesticide residues in water environments remains a challenging issue. In this paper, we prepare Fe3O4/MOF-867 composites using the hot solvent method, and Au+ is reduced to Au NPs by the reducing agent and attached to the film of Fe3O4/MOF-867 composites by the addition of APTES as a linker to synthesize the Au/Fe3O4/MOF-867 SERS substrates. Then, we change the Fe3O4 content and the concentration of the reducing agent to obtain the optimal substrate. The substrate has a detection capability of up to 10−9 M for probe molecule R6G and the RSD is less than 5%, which demonstrates that the substrate has excellent SERS effect and reproducibility. In addition, the Au/Fe3O4/MOF-867 SERS substrates have been applied for the determination of thiram in lake water samples, with its limit of detection (LOD) up to 3.8 × 10−10 M. The Au/Fe3O4/MOF-867 SERS substrates can quickly and efficiently collect target analytes by magnetic enrichment, have high SERS performance, and have great potential for the rapid and sensitive detection of pesticide residues and other pollutants in the environment.

Construction of Ag nanoflowers@ZIF-8 core-shell nanocomposite for sensitive SERS detection of hazardous substance in river water

The presence of hazardous substance in river water poses a severe threat to both the ecological environment and human health. Therefore, designing and preparing highly sensitive SERS platform for monitoring the hazardous substance is of great significance. Herein, the Ag nanoflowers (NFs)@ZIF-8 core-shell nanocomposite was synthesized and utilized as SERS substrate. Using crystal violet as model molecule, this substrate achieved a detection limit of 10−10 M and superior uniformity with relative standard deviation of less than 15 %, and the enhancement factor (EF) for crystal violet was calculated about 4.37×106. Besides, the SERS signal only showed a slight attenuation after 3 months storage. As a demonstration, the SERS platform achieved sensitive detection of two hazardous substances thiram and methylene blue with detection limits of 10−7 M and 10−8 M. And the recoveries of SERS detection for thiram and methylene blue in river water were between 70 % and 182 %. The electromagnetic enhancement provided by Ag NFs and the enriching effect of ZIF-8 shell collectively contribute to the excellent performance of the Ag NFs@ZIF-8 SERS platform. This work delivers a promising strategy for constructing hybrid SERS platform for highly sensitive detection.

Quartz fiber supported Ag nano-islands as flexible SERS substrate with stable distributed “hot-spot” in rapid detection of pesticide residue

Island-shaped Ag nanoparticles are prepared under the support platform of quartz fabric by a simple chemical deposition method. The prepared flexible SERS substrate in this study demonstrates highly sensitive, excellent signal reproducibility and stability. The enhancement ability can be adjusted by varying concentration of Ag+ during synthesizing process, which would lead to the variation of size and gaps of Ag nanoparticles, thus affecting the LSPR effect. Moreover, the prepared SERS substrate shows great practical potential in rapid detection of contaminated fruit with different sampling method.

Sandwich-like CuNPs@AgNPs@PSB SERS substrates for sensitive detection of R6G and Forchlorfenuron

The development of a highly sensitive, synthetically simple and economical SERS substrate is technically very important. A fast, economical, sensitive and reproducible CuNPs@AgNPs@ Porous silicon Bragg reflector (PSB) SERS substrate was prepared by electrochemical etching and in situ reduction method. The developed CuNPs@AgNPs@PSB has a large specific surface area and abundant “hot spot” region, which makes the SERS performance excellent. Meanwhile, the successful synthesis of CuNPs@AgNPs can not only modulate the plasmon resonance properties of nanoparticles, but also effectively prolong the time stability of Cu nanoparticles. The basic performance of the substrate was evaluated using rhodamine 6G (R6G). (Detection limit reached 10−15 M, R2 = 0.9882, RSD = 5.3 %) The detection limit of Forchlorfenuron was 10 μg/L. The standard curve with a regression coefficient of 0.979 was established in the low concentration range of 10 μg/L −100 μg/L. This indicates that the prepared substrates can accomplish the detection of pesticide residues in the low concentration range. The prepared high-performance and high-sensitivity SERS substrate have a very promising application in detection technology.

Ag-modified CuO cavity arrays as a SERS-electrochemical dual signal platform for thiram detection

Rapid and sensitive determination of pesticide residues in fruits and vegetables is critical for human health and ecosystems. This paper used an Ag-modified CuO sphere-cavity array (CuO@Ag) electrode as a thiram SERS/electrochemical dual readout detection platform. Numerous Raman “hotspots” generated by uniformly distributed silver nanoparticles, charge transfer at the CuO@Ag interface, and the formation of Ag-thiram complexes contribute to the significant enhancement of this SERS substrate, which results in excellent SERS performance with an enhancement factor up to 1.42 × 106. When using SERS as the readout technique, the linear range of the substrate for thiram detection was 0.05–20 nM with a detection limit (LOD) of up to 0.0067 nM. Meanwhile, a correlation between the value of change in current density and thiram concentration was established due to the formation of stable complexes of thiram with Cu2+ generated at specific potentials. The linear range of electrochemical detection was 0.05–20.0 μM, and the detection limit was 0.0167 μM. The newly devised dual-readout sensor offers notable sensitivity and stability. The two signal readout methods complement each other in terms of linear range and detection limit, making it a convenient tool for assessing thiram residue levels in agro-food. At the same time, the combination of commercially available portable equipment makes on-site monitoring possible.

Nanoscale Kirkendall effect induced void formation in Au–Ag nanostructures and their application as SERS substrate

Triangular-shaped silver nanostructures were synthesized via a seed-mediated two-step method. A galvanic replacement reaction coupled with the Kirkendall effect was employed to transform Ag nanostructures into porous Au–Ag structures having voids at the nanoscale. Compared with previous reports, the medium and the binding agent used in the synthesis of silver nanoparticles employed as templates play a vital role in determining the extent of nanoscale voids formed due to the Kirkendall effect. Raman activity of these porous structures was tested with crystal violet as the probe molecule, and it was found that the Raman enhancement factor varies with cathode concentration.

Bacterial cellulose membrane SERS substrate for in-situ reduction of gold nanoparticles for detecting TNF-α

In this study, we developed a two-dimensional bacterial cellulose nanogold substrate via in situ reduction and utilized a sandwich model with 4-MBN as a Raman reporter for sensitive detection of TNF-α. TNF-α, a critical cytokine in various diseases, was detected in a broad range (10−8 to 10−4 mg/mL) with a remarkable detection limit of 0.35 pg/mL. The assay exhibited excellent specificity, with a 98 % recovery rate for serum samples at 5 × 10−7 mg/mL. This method shows promise for precise TNF-α determination in complex samples, suggesting its potential for diagnostic and research applications.

In situ growth of silver nanoparticles on alkali-treated cotton swabs as a cheap and highly sensitive SERS substrate for rapid detection of food additives

Surface-enhanced Raman scattering (SERS) technique has become a powerful and useful tool for detecting chemical substances in the field of food safety detection. However, the development of a highly sensitive, reliable, inexpensive and portable SERS substrate is still a great challenge. Herein, we developed a cheap, reliable and portable SERS sensor through in-situ growth of silver nanoparticles (AgNPs) on alkali-treated cotton swabs (CS) without using any expensive materials and complicated synthesis methods. The morphological analysis demonstrates that silver nanoparticles were highly homogeneous and controllably grown on the surface of cotton fibers. The effect of AgNPs content on the SERS performance of AgNPs@CS substrate is systematically investigated. The optimal AgNPs@CS SERS sensor not only achieves high detection sensitivity of 1.0 × 10-9 M for toxic malachite green but also exhibits high enhancement factor up to 3.2 × 106 and excellent signal homogeneity (relative standard deviation, RSD = 9.3 %). In addition, the SERS performance of the sensor toward food additive of indigo exhibits good linear correlation during the range of 1.0 × 10-5 to 1.0 × 10-9 M. Attributed to the good mechanical properties, flexibility and portability of the cotton swabs, a rapid and direct identification of indigo residues on the surface of edible amaranth using AgNP@CS SERS sensor was realized through a feasible and effective wipe-and-read route. The inexpensive, accessible and portable AgNP@CS SERS substrates demonstrate great potential in the identification of toxic and hazardous substances in the field food safety detection.

Refining shape and size of silver nanoparticles using ion irradiation for enhanced and homogeneous SERS activity

We present green synthesis of silver nanoparticles in water using unirradiated and Ag15+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{15+}$$\\end{document} ion irradiated phytoextracts of Bergenia Ciliata leaf, Eupatorium adenophorum leaf, Rhododendron arboreum leaf and flower. The use of different plant extracts and their subsequent ion irradiation allow for successful refinement of nanoparticle size and morphology. Due to changes in reducing and capping agents the nanoparticle surface functionalization also varies which not only controls the morphology but also allows for surface oxidation and aggregation processes. In this work, we have synthesized silver nanoparticles which exhibit sizes in the range from 13 to 24 nm and having shapes like spherical, quasispherical, trigonal, hexagonal, cylindrical, dendritic assemblies, and porous nanoparticles. Owing to changes in the size and shape of the nanoparticles, their direct bandgap (2.05 eV - 2.48 eV) and local surface plasmon resonance (420 nm - 490 nm) could also be tuned. These nanoparticles are examined as SERS substrates, where their enhancement factors, limit of detection for methylene blue, and SERS substrate homogeneity have been tested. It has been observed the nanoparticles synthesized using unirradiated plant extracts present an enhancement factor of 106\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^6$$\\end{document} with a limit of detection 10-8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-8}$$\\end{document} M. Whereas nanoparticles with refined morphology and shapes upon irradiation present high enhancement factors of >107\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^7$$\\end{document} and detection limit down to 10-9\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-9}$$\\end{document} M. In addition, uniformity in Raman spectra over the SERS substrates has been obtained for selected Ag NPs substrates synthesized using irradiated extracts with minimum relative standard deviation in enhancement factor < 12%.

Ag@Au yolk shells decorated onto silica spheres for enhanced plasmonic applications

Silica surfaces covered with a homogenous layer of metal nanoparticles exhibit superior plasmonic properties when compared with pristine colloidal counterparts, as they have higher scattering probability with enhanced potential utility. Precise galvanic replacement reactions performed on such sacrificial templates are of great interest. Herein, we demonstrate the robust formation of Ag@Au yolk shells decorated onto the dielectric silica spheres via a direct one-step galvanic replacement procedure, evidently initiating the deposition of Au onto low surface energy Ag facets (prefixed onto the silica spheres), resulting in a disjointed framework of compact dealloyed metal lobes, wherein their facets remain smooth enough with a high degree of crystallinity and exhibit maximal porosity. Our combined spectroscopic data analyses corroborate the plausible mechanism governing solely the formation of Ag@Au core-shell onto the silica spheres rather than their hollow counterparts. Furthermore, we made the respective monolayer films using the well-known air-water interface self-assembly technique, which allowed us to easily decorate different substrates with a uniform array of these surface-coupled metal nanoparticles. Enhanced refractive index (RI) sensing applications based on the sensitivity and FOM (figure of merit) calculations demonstrate the versatile nature of our synthetic protocol for direct synthesis of optical metamaterials along with their intriguing light-matter interactions, in general. Also, the plasmonic vector field of 2-D assembled nanoparticle monolayer displays intrigued SERS enhancement of crystal violet dye when compared with their respective drop-casted films, thus establishing a novel method for producing diverse meta-structures based efficient SERS substrates with promising applications in ultrasensitive chemical and biological sensing.

INFLUENCE OF THE REDUCING AGENTS ON MORPHOLOGY AND PROPERTIES OF SIVER STRUCTURES ON PAPER

Abstract. A paper-based SERS substrate with tunable plasmonic properties and excellent flexibility has been applied in various fields. These SERS substrates were prepared using a direct chemical reduction synthesis method for the present work. The isotropic and anisotropic morphology of silver structures on cellulose paper fiber were controlled by the types of reducing agents: (1) sodium borohydride (NaBH4), (2) ascorbic acid (L-AA), (3) glucose, (4) formaldehyde (HCHO). The plasmon characterization of silver structures on paper was systematically investigated. The fabricated paper-based SERS substrates were used to detect melamine in an aqueous solution and determine the influence of type reducing agents on the enhancement factor (EF) and signal uniformity of SERS substrates.

Flexible SERS substrate with tunable gap based on laser-induced reduction

Flexible SERS substrate with tunable gap based on laser-induced reduction

Diatomite-Based, Flexible SERS Immunosensor Platform for Rapid, Specific, and Sensitive Detection of Circulating Cancer-Specific Protein Biomarkers in Serum Using Raman Probes.

Cancer is one of the most actively researched diseases having a high mortality rate when not detected at an early stage. Thus, rapid, simultaneous, and sensitive quantification of cancer biomarkers plays an important role in early diagnosis, with patient impact to disability adjusted life years. Herein, a diatomite-based SERS flexible platform for the rapid and sensitive detection of circulating cancer-specific protein biomarkers in serum is presented. In this approach, diatomite/AgNPs strips with maximum SERS activity prepared using the layer-by-layer (LbL) technique were modified with specific antibodies, and specific antigens (HER2, CA15-3, PSA, and MUC4) were captured and detected. By using Raman probes specific to the captured antigens in serum, a SERS limit of detection (LOD) of 0.1 ng/mL was measured (calculated LOD < 0.1 ng/mL). This value is lower than the cutoff amount of cancer antigens in the person's blood. The specificity for the antigens of each antibody was calculated to be higher than 95%. As a result, an immunosensor for rapid detection of cancer biomarkers in serum with good specificity, high sensitivity, good reproducibility, and low cost has been demonstrated. Overall, we show that the prepared diatomite-based SERS substrate with a high surface-to-volume ratio is a useable platform for immunoassay tests.

High‐resolved surface‐enhanced Raman scattering on Ag@TiO2 plasmonic nanostructure

AbstractSurface‐enhanced Raman scattering (SERS) is an ultrasensitive spectroscopic analysis technique widely used for molecule detection. However, manufacturing uniform, stable, and ultrasensitive substrates remains a challenge for the practical application of the SERS technology. Precious metals and semiconductors have been proved to be attractive and universal for SERS detection. In this work, a facile strategy is applied to prepare uniform three‐dimensional (3D) Ag@TiO2 nanostructures as SERS sensors. The Scanning electron microscopy and X‐ray photoelectron spectroscopy results indicate that silver nanoparticles are uniformly deposited into the pores of the TiO2 nanocavity arrays. The 3D hybrid substrate presents highly sensitive SERS signals of 4‐mercaptobenzoicacid (4‐MBA) with a detection limitation as low as 10−17 M. To prevent the oxidization of Ag and keep the activity of the film, a polymer mask was deposited on the SERS substrate and brought about excellent stability after weeks of reserving in air. In a nutshell, a SERS substrate with a high sensitivity and stability as well as good uniformity has been successfully developed in this work, which has a potential application for high‐precision SERS detection.

HAuCl4/K4Fe(CN)6 reaction mediated silver nanosol as SERS substrate for robust detection of malachite green residue in seafood

Irreproducibility is considered as a significant obstacle to the widespread use of surface enhanced Raman spectroscopy (SERS) as a sensing platform. However, in terms of the SERS performance in applications, less attention has been paid on the stability, i.e., repeatability and reproducibility compared to sensitivity. Here, based on HAuCl4/K4Fe(CN)6 reaction and silver nanosol (Ag NS), a reaction mediated SERS (R-SERS) platform was proposed for the detection of malachite green residue (MG) in aquatic products, aiming to improve both the sensitivity and stability of SERS. Wherein, the HAuCl4/K4Fe(CN)6 reaction produced Au0 grows on Ag NPs and provided additional “hot spots” to enhance signal intensity. Meanwhile, the reaction system released cyano group (-C≡N) will cap on the surface of Ag or Au NPs and act as an internal signal at ∼2100 cm−1 to adjust the background signal. As a proof of principle, adenine (Ade, 730 cm−1), ceftriaxone (Cef, 1345 cm−1) and MG (1170 cm−1) were selected as targets to discuss the detection performance, with linear ranges of 0.1 ∼ 20 μM, 0.1 ∼ 10 μM and 0.1 ∼ 2 μM and limit of detection (LOD, 3σ/M) of 0.079 μM, 0.050 μM and 0.032 μM, respectively. In practical applications, MG residue in aquatic products were detected with the recoveries ranged from 85 % to 98 % and the coefficient of variations of intra-assay below 6.6 %. The R-SERS platform, therefore, was demonstrated to enhance SERS intensity and stability with in situ growth of label on Ag NPs, suggesting its potential applications in SERS sensing.

Silica monolayer isolation of electrodeposited SERS substrate and online probing of molecule adsorption onto mineral microparticles in relation to flotation

In the minerals processing industry, the surface chemistry of mineral particles and its real-time detection can significantly enhance process performance, and ultimately leading to automotive and intelligent control. The adsorption of collector molecule onto bulk mineral specimens could be investigated with the help of shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS). However, this method is unsuitable for the online detection of particles fluid consisted of micro-sized chalcocite that encountered in industrial production processes. In this work, a novel strategy of shell-isolated nanoparticles synthesis by electrodeposition of gold nanoparticles film and isolation of this film with crosslinked silica monolayer was proposed. The adsorption of 2-mercaptobenzothiazole (MBT), a typical flotation collector, onto a copper sulfide mineral, chalcocite was measured in-situ with the help of such a SERS substrate. Enhancement factors of 106–107 was calculated based on an idealized model. Furthermore, we discussed the stability of the silica isolation monolayer under high-power laser irradiation.

A Three-Dimensional Hydrophobic Surface-Enhanced Raman Scattering Sensor via a Silver-Coated Polytetrafluoroethylene Membrane for the Direct Trace Detection of Molecules in Water.

We report a three-dimensional (3D) SERS substrate consisting of a silver nanoparticle (AgNP) coating on the skeleton-fiber surfaces of a polytetrafluoroethylene (PTFE) membrane. Simple thermal evaporation was employed to deposit Ag onto the PTFE membrane to produce grape-shaped AgNPs. The 3D-distributed AgNPs exhibit not only strong localized surface plasmon resonance (LSPR) but also strong hydrophobic performance. High-density hotspots via silver nano-grape structures and nanogaps, the large 3D interaction volume, and the large total surface area, in combination with the hydrophobic enrichment of the specimen, facilitate high-sensitivity sensing performance of such a SERS substrate for the direct detection of low-concentration molecules in water. An enhancement factor of up to 1.97 × 1010 was achieved in the direct detection of R6G molecules in water with a concentration of 10-13 mol/L. The lowest detection limit of 100 ppt was reached in the detection of melamine in water. Such a SERS sensor may have potential applications in food-safety control, environmental water pollution monitoring, and biomedical analysis.

Piezoelectric modulated charge transfer in SERS substrate based on black phosphorous-graphene oxide/polyvinylidene fluoride

Electrical modulation is considered to be effective in improving the localized electromagnetic strength of surface enhanced Raman scattering substrates (E-SERS). In this field, polyvinylidene fluoride (PVDF) as a versatile piezoelectric matrix has been extensively employed to construct E-SERS substrates by combining with noble metals. However, there is nearly no exploration of the impact of the piezoelectric effect on the charge transfer within bare semiconductors, which will greatly expand the variety of E-SERS substrates. In this study, a novel semiconductor-based E-SERS substrate was developed by integrating black phosphorous (BP)-graphene oxide (GO) composite with a PVDF matrix. A significant SERS signal amplification was achieved when subjected to mechanical stress. Such amplification was owing to the improvement of charge transfer efficiency facilitated by the external force-triggered polarization charge, which was proved by the photocurrent test. The piezoelectric effect was verified to boost chemical enhancement and the semiconductor-based E-SERS substrate was capable of achieving high sensitivity.

Construction of dense film inside capillary wall and SERS application research

The high-density particle distribution in capillary was a crucial factor for enhancing SERS properties and a difficult point in the preparation process. The direct high-temperature method was used to fuse the particles and form a uniform and dense particle distribution on the capillary's inner wall, providing a foundation for enhancing Raman signals. The prepared capillary SERS substrate strongly enhances the rhodamine 6G (R6G) signal, and the RSD values of several characteristic peaks of R6G are about 10 %, demonstrating high sensitivity, uniformity, and stability. Using capillary SERS substrate for detecting goat serum. Embedding precious metal particles into capillary SERS substrate can effectively encapsulate the tested liquid and avoid contamination, which improves the disadvantage of traditional substrates exposing the liquid to air. The prepared capillary SERS substrate could be used for field and biomedical sensitivity detection, providing a theoretical and experimental basis for developing the capillary SERS substrate.

SERS-electrochemical dual-mode detection of microRNA on same interface assisted by exonuclease III signal transformation

Dual-mode sensing has attracted more attentions which provide more accurate and reliable approach of cancer-related biomarkers. Herein, we developed a novel SERS/electrochemical dual-mode biosensor for miRNA 21 detection based on Exo III-assisted signal transformation. Firstly, the Au NPs were deposited on electrode as SERS substrate and Mn3O4/S4(DNA signal strand) was modified on Au NPs/S5 by the DNA strands S5-S4 pairing principle as hydrogen peroxide catalyst, leading to an obviously high DPV electrical signal without Raman signal. Subsequently, the presence of miRNA 21 will activate the Mn3O4/S4 to be decomposed under exonuclease III-assisted process, then the S3′ chains modified with Raman molecular Cy3(Cy3-S3′) is continuously connected to the Au NPs/S5 by DNA stands S5-S3′ pairing principle, leading to the Raman signal response and DPV signal reduction. The biosensor shows good linear calibration curves of both SERS and electrochemical sensing modes with the detection limit of 3.98 × 10−3 nM and 6.89 × 10−5 nM, respectively. This work finds an ingenious mode for dual detection of microRNA on a same interface, which opens a new strategy for SERS and electrochemical analysis.